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2 Simulation and Virtual Prototyping are seen as key disciplines for achieving progress in engineering and science in the 21st century. In this light, EnginSoft is hosting its International Conference 2009 CAE Technologies for Industry on 1-2 October in Bergamo, Northern Italy - concurrently with the ANSYS Italian Conference This occasion has become one of the leading events in Europe for all those involved in CAE, with record attendances in recent years. 1 st -2 nd October 2009 Bergamo - Centro Congressi Giovanni XXIII Our 2009 edition will present the diversity and impact of CAE Technologies to an international audience of users from various industries with different backgrounds, developers, scientists and researchers. The two Conferences will offer a highly innovative platform for interaction and exchange of knowledge, development and application results. Moreover, they will reveal convincing visions for the future of engineering simulation in industry, research and the academia. The program will feature presentations from leading experts and key companies from around the world highlighting applications in automotive, aerospace, energy, marine, oil&gas, consumer goods, environment, biomedicine and other areas. In several product update sessions, conference attendees will hear about the latest developments of state-of-the-art CAE software encompassing: ANSYS - ANSYS CFX - ANSYS Fluent - ANSYS ICEM CFD - modefrontier - ANSOFT - Flowmaster - MAGMASOFT - FORGE - FTI - THIRD WAVE SYSTEM - LS-DYNA - ESACOMP A Demo Room will be available throughout the conference where attendees will meet for interactive discussions and live demos of the latest software releases. The official language of the EnginSoft International Conference will be English. To complete the information flow during the two conference days, a large accompanying exhibition will see the world's leading solution providers showcasing products and services covering all aspects of CAE technologies and their successful implementation. As a tradition, delegates and exhibitors will use the exhibition as an international networking forum to gain new insights, share experiences and to find new business opportunities. Follow the Sound of Innovation - Be Inspired about CAE - Come and meet us in Bergamo! Further information: EnginSoft Marketing Department Dott.ssa Luisa Cunico Ph EARLY BIRD REGISTRATION UNTIL 31 JUNE EVENT ORGANIZED BY: GOLD SPONSOR: SOME EXHIBITORS: PATRONAGE:

7 Newsletter EnginSoft Year 6 n 2-7 EnginSoft Flash Ing. Stefano Odorizzi General Manager EnginSoft Summertime always sees the EnginSoft teams committed to the planning of our annual International Conference which carries the motto: CAE Technologies for Industry. We are delighted to announce that the Program of 1st & 2nd October could already include an incredible number of presentations which we received in response to our Call for Papers. This is exceptionally positive feedback from the simulation community despite difficult times, reduced travel budgets and other constraints. The 2009 Program will feature contributions from speakers from around the world reflecting the diversity and impact of CAE Technologies. The EnginSoft International Conference and ANSYS Italian Conference 2009 will offer a highly innovative platform for interaction and exchange of CAE and VP knowledge, development and application results. Moreover, they will reveal convincing visions for the future of engineering simulation in industry, research and the academia. We are proud to welcome Microsoft and E4 Computer Engineering as the first Gold Sponsors and NAFEMS International as the official Patron of the 2009 Conferences in Bergamo. Among the software which will be presented, also in the large accompanying exhibition, are: ANSYS - ANSYS CFX ANSYS Fluent ANSYS ICEM CFD modefrontier ANSOFT - Flowmaster MAGMASOFT FORGE FTI THIRD WAVE SYSTEM LS-DYNA ESACOMP This edition of the Newsletter informs our readers about European Saloon Car Racing Made in Sweden with the C30 Volvo Racing Car running on 100% E85 Bio-Ethanol and Aerodynamic optimization performed with modefrontier. Basics of the technology are reflected in the articles on Handwritten pattern recognition with modefrontier and The EnginSoft Newsletter editions contain references to the following products which are trademarks or registered trademarks of their respective owners: ANSYS, ANSYS Workbench, AUTODYN, CFX, FLUENT and any and all ANSYS, Inc. brand, product, service and feature names, logos and slogans are registered trademarks or trademarks of ANSYS, Inc. or its subsidiaries in the United States or other countries. [ICEM CFD is a trademark used by ANSYS, Inc. under license]. (www.ansys.com) modefrontier is a trademark of ESTECO EnginSoft Tecnologie per l Ottimizzazione srl. (www.esteco.com) Flowmaster is a registered trademark of The Flowmaster Group BV in the USA and Korea. (www.flowmaster.com) the effective use of the program for Statistical Applications and such interesting questions as, what is the highest, lowest or richest city in Italy? With the support of Automotive Lighting Italy, we could create a thorough article on Modeling of condensate formation and disposal inside an automotive headlamp which addresses an important but rarely covered topic in the automotive engineering field. News from the modefrontier network come from APERIO Spain and two successful Seminars on Product Process Integration held in the Barcelona and Bilbao regions. EnginSoft GmbH reports a growing demand for multiobjective optimization in Germany and Switzerland and sees clear benefits for R&D. EnginSoft France showcased its flagship products modefrontier V4.1 and Flowmaster V7, to the aerospace industries at this year s International Paris Air Show. As always, we include a detailed Event Calendar for our readers with information on where EnginSoft can be met in Europe at the various events we are attending or hosting. Last but not least, an absolute premiere: The Japan Column - which will, from now on, bring to our readers exceptional insights into the Japanese CAE Culture including news, events and lots of interesting facts and background knowledge. I hope you will join me in discovering more about MONODUKURI, Japanese engineering spirit and traditional manufacturing. The Land of the Rising Sun, its people and their culture, are marvelous at delivering quality to a product and to new developments by applying technology, regardless of whether it concerns CAE or BONSAI (the art of aesthetic miniaturization of trees) and KAISEKI (a type of art that balances the taste, texture, appearance and colors of food) The editorial team of the Newsletter invites you to enjoy the various contributions and welcomes any comments or ideas you may have. Please mark your diary for the 1st & 2nd October and follow our publications on the EnginSoft International Conference, one of the largest events for CAE users in Europe. We hope to see you in Bergamo! Stefano Odorizzi Editor in chief MAGMASOFT is a trademark of MAGMA GmbH. (www.magmasoft.com) ESAComp is a trademark of Componeering Inc. (www.componeering.com) Forge and Coldform are a trademark of Transvalor S.A. (www.transvalor.com) AdvantEdge is a trademark of Third Wave Systems. (www.thirdwavesys.com) LS-DYNA is a trademark of Livermore Software Technology Corporation. (www.lstc.com) For more information, please contact the Editorial Team

11 The design and verification of a cylinder head is usually the most critical application of the structural optimization of the assembly behavior. Newsletter EnginSoft Year 6 n 2-11 Thermal-structural analysis of a Cylinder Head using the Workbench Platform. A unique calculation environment for different vertical codes Nowadays, complex geometries and different schematization requirements due to CFD and structural issues are causing an infinite number of problems. These technical difficulties are mainly related to different meshing topologies and to the single nonlinearity of each numerical code. This article describes the flexibility of the Workbench Platform, a technical approach that is characterized by its capability to connect the different codes and, at the same time, to point out the single peculiarities of each code. Figure 2: the simulation tree A CFD analysis using the Vectis code was performed. The results with regard to convection coefficients and bulk temperatures were mapped on a FEM thermal meshing generated in the ANSYS Simulation environment. Then, these results were used for the structural non-linear analysis performed in ANSYS. At the same time, a pilot project has been developed with the aim to verify the efficiency of the Workbench 12.0 platform as a unified environment. All the technical activities of the project were focused on a fluid dynamic, thermal-structural analysis applied to an automotive cylinder head. The analysis has been completely performed with the ANSYS Workbench 12.0 platform. The engineers involved in the work could take advantage of the following Workbench capabilities: Figure 3: the customized interface: link to the remapping macros Multiphysics platform Tool for integration of different technologies (external fluid dynamic software, ANSYS Thermal, ANSYS Mechanical) Tool for advanced meshing and solving of models with a high number of degrees of freedom. Figure 1: Logical flux from CFD to thermal structural analysis When we look at the details of the project work, they can be best described and summarized as follows: The logical flux of the analysis of a cylinder head which starts with the CFD results of the combustion chamber and the cooling system obtained by the Vectis code, transfers the information from the thermal analysis to the structural pre-stressed non-linear analysis in ANSYS. The added-value of this project is the customization of the Workbench interface which, in fact, realizes an automatic link to the Vectis results and ensures the possibility of remapping the fluid dynamic results on the thermal-structural mesh. The latter is completely different from the CFD model.

12 12 - Newsletter EnginSoft Year 6 n 2 Figure 4: thermal-structural coarse mesh-cfd fine mesh First step: From CFD results to thermal conditions So far, the traditional working process has been to perform a unique mesh for the CFD and thermal-structural analysis in order to be able to remap the fluid dynamic results, in terms of bulk temperatures and convective coefficients, on the mechanical mesh. Hence, the thermal-structural model had to be created with the same topology as the CFD model which caused long modeling times. Furthermore, the software used for the fluid dynamic, thermal and structural analysis, in many cases, belonged to different families of software (ANSYS, Nastran, Abaqus, Vectis ). This scenario caused considerable increases in costs and a number of problems concerning interfaces and other interpolations. Owing to the newly introduced procedure, it has become possible to interpolate, in an automatic way, the fluid dynamic results on the mechanical mesh which is completely different (from a topological point of view) to the CFD grid. This led to a severe reduction of modeling time and number of obtained elements (from a fine CFD mesh to a coarse thermo-structural model). The only constraint for the proper interpolation of the CFD results is to have a proper spatial positioning of the thermal structural model compared to the fluid dynamic model. In other words, the two geometrical models must have Figure 5: Equivalent Von Mises stress in the last time step the same spatial position. Thanks to the new customization realized with the j-script and ANSYS APDL language, it is now possible to apply the correct fluid dynamic loads simply by taking into account the Vectris results file and by creating a component with those nodes that require the interpolation. In this way, the same model can be used to perform the thermal analysis and the structural pre-stressed analysis, saving time during the preparation and the solution of the model, thus avoiding further phases of interpolation of temperature values for the structural model. Second step: From thermal analysis to structural analysis The results of the thermal analysis, performed with bulk temperature and convective coefficient evaluated with the CFD method, are transferred to the structural model without any further interpolation thanks to the same FEM model which can be used for both analyses. In this specific case, the analysis was carried out in several steps to take into account the pre-heat stress, and to subsequently model both: the phase of bolts clamping and the phase of the valve seat clamping with the head. The last step represents the real loading phase linked to the pressure in the combustion chamber. Both the non-linearity related to material yielding as well as the nonlinearity related to contacts are considered. This procedure is automatic and it requires limited efforts by the user. Therefore, it is very easy to perform another analysis with the same logical flux, but with different geometries or under different fluid dynamic conditions. It is also possible to utilize the model and/or the results of the structural analysis to perform a fatigue evaluation or a creep calculation. For further information: Ing. Valentina Peselli - EnginSoft

13 Newsletter EnginSoft Year 6 n 2-13 Modeling of condensate formation and disposal inside an automotive headlamp An automotive headlamp is an environment with high thermal and low mass exchanges with the external environment; for these reasons, humidity can accumulate inside the headlamp and can condensate on the lens. A headlamp design can be produced only if, under severe thermal conditions, all the formed condensate is disposed in a fixed time. The combined use of experimental studies INTRODUCTION Automotive design has always been driven by aesthetic choices. In this context, technology plays an important role to meet the challenges linked to design solutions and the requirements of car stylists and automotive designers. Aerodynamic and curved shapes, new materials and coatings often contrast with economic and production needs. Headlamps play a key role: located on the front of the car, lighted, with sophisticated technological solutions such as LED, light-guide and adaptive lighting systems, they have always been used by stylists to enhance aesthetics. On the other hand, mechanical and optical designers have to satisfy many functional requirements. Crash and safety tests, thermal behavior, and obviously lighting performances are only few of a great number of technical needs. The right solution for the conjugation of aesthetics and technologies involving cost and production requirements is not always easy to find and often new problems appear during project development. Figure 1: comparison of an old-fashioned glass headlamp (left) and a new transparent plastic headlamp (right) and numerical modeling is an important tool to optimise headlamp design and to produce high performance headlamps. Experimental studies are to be performed in climatic chambers under highly controlled conditions. On the other hand, long transient numerical simulations are to be performed on large meshes in order to capture the relevant physics of the problem. A new numerical method has been implemented in order to study this problem and has been applied to real case headlamp designs providing good agreement between numerical and experimental results. Something similar happens with condensate formation and disposal. The increase of moulding capabilities leads to a massive production of large transparent plastic lenses. Until few years ago, lenses were typically designed using glass and covered by optical prism to obtain the correct light distribution (see Figure 1). Curved shapes and transparent surfaces opened a new world for style solutions, but a transparent lens lets the eye go into the headlamps (see Figure 1). Today, the observer has a free view of the inside of the headlamp highlighting even the smallest optical fault, any thermal damage of the inner components and the possible presence of water droplets. In Figure 2, an example of condensate on a headlamp lens is shown. The presence of condensate inside the headlamp is perceived by the customer as a lack of quality and reliability. Figure 2: condensate on a prototype specifically designed for enhancing condensate formation. Left: prototype mounted on the car. Right: details of the prototype

14 14 - Newsletter EnginSoft Year 6 n 2 A possible solution for condensate formation is seen in anti-fog coating. Here, a layer of hydrophobic material painted on the inner side of the lens prevents the water to stick onto the plastic walls. Another solution is the use of a hydrophobic membrane applied to large vent holes. In this way, high air flow rates are allowed to pass through the membrane but the headlamp is kept sealed with respect to humidity. The drawbacks of these methods are the strong impacts on the cost per piece and on the cycle-time. These solutions are generally applied to luxury and highperformance cars where cost and production volume are not so relevant. The most used solution for decreasing condensate quantity and disposal time is represented by the optimization of inner air flows and of temperature distribution on the main lens. Typically, at least two vent holes are located on the headlamp housing. In order to optimize their efficiency, it is important to find the right numbers and locations by performing numerical and physical tests during the pre-industrialization phase. In Figure 3, an example of vent holes in the headlamp housing is shown. Until today, the right solution to condensate formation has always been sought by trials and error. This implies a great increase in time and costs. In this context, the use of appropriate numerical methods and test rooms becomes a strategic tool for decreasing production time and cost and, in the near future, for optimizing headlamp design with respect to condensate formation and disposal. From a fluid-dynamic point of view, an automotive headlamp can be considered as a cavity with low massflow interaction but high thermal interaction with the external environment. One wall of the cavity, the lens, is transparent while the others are opaque. Inside the headlamp there are one or more lamps and a number of components: reflectors, screens, caps, connectors, pipettes, etc. These components are used for the functionality of the headlamp but, in the meanwhile, play a fundamental role in the thermo-fluid-dynamic behavior of the fluid inside the headlamp which is a mixture of air and water vapour. The headlamp can undergo phenomena of heating and cooling because of internal and external heat sources. The external heat sources or sinks are represented by the external environment temperature or by the heating coming from the engine. The internal heat source is represented by the switched-on lamp which heats up the surrounding fluid and emits radiation. Since Figure 3. example of vent holes on the headlamp housing the fluid inside the headlamp is composed of a mixture of air and water vapour, it changes density because of thermal evolution. Density differences are the cause of internal convective motions which are always laminar. Since temperature is, in final analysis, the engine of the motion of the internal fluid, it is important to precisely and accurately characterize all the components of the headlamp. They are to be characterized both from a thermal and an optical point of view, in order to model temperature, heat transfer to surrounding fluids, radiation absorption, emission and reflection. Moreover, the assembly of all components delimits the space where fluid can flow, and hence determines the motion field inside the headlamp. All components should be modelled with a geometrical detail adequate to the level of accuracy desired for the fluid-dynamic results. On the other hand, a great geometric detail leads to a large mesh and hence to large computational costs. The right trade off between geometric details and computational costs has to be achieved. In addition to this, temperature evolution of the headlamp may cause water phase changes; in particular it may cause water condensation and evaporation on the lens which is a main issue for headlamp producers and the target of the present work. The problem to be studied is a typical multi-phase problem for which it is important to properly describe the phase change between liquid water and water vapour. Given this problem, it is important to properly describe the natural convection velocity field due to different density of fluid masses inside the headlamp. For this reason, it is important to account for gravity and buoyancy effects in the fluid. Since the motion field is

15 Newsletter EnginSoft Year 6 n 2-15 Figure 4: ALIT condensate test room (left) and engine box mock-up inside the room (right) driven by natural convection, the flow is laminar and no turbulence model is used. Another important phenomenon to be modelled is the heat transfer between walls and fluid, between different fluid masses and, particularly, the latent heat absorbed by water evaporation and released by vapour condensation. Finally, when a switched-on lamp is considered, thermal radiation is to be accounted for. In order to study the condensate phenomenon inside an automotive headlamp, a series of experimental and numerical tests have been performed on specifically designed prototypes in which the condensation process was enhanced. In what follows, one of these tests is presented in details. EXPERIMENTAL STUDIES History of condensate tests Headlamp reliability verification with respect to condensate effects started in the early 90, with the introduction of clear lenses and plastic materials. Soon afterwards, customer specifications included the same. The first step was the introduction of some verification criteria on the basis of pre-existent tests. These criteria involved the absence of water droplets inside the headlamp during the standard sealing and rain tests. Nevertheless, these tests were not conceived to check the specific worst condition for the condensate formation but usually to test tropical rain and ford conditions. Indeed, they were mainly focused on discovering any eventual lack on the headlamp sealing and not on the inner air flux optimization. A typical tropical rain test is performed at ambient temperature higher than 24 C which is far from the cold and foggy conditions for condensate formation. Consequently, specific tests, more and more severe, have been performed to understand and prevent any possible defects. Obviously, this process required some years to reach a deeper understanding of the phenomena and to introduce some technical solutions, such as, for example, the introduction of vent pipes, hydrophobic membrane and anti-fog coating. The first condensate tests were driving-tests, a powerful but hardly reproducible method for taking into account all the variables of the system, such as interactions between engine components and headlamp. The influence of the external air properties, such as temperature and humidity did not allow to schedule a test campaign. It then became necessary to perform tests in a controlled environment, such as a wind tunnel facility using a full scale vehicle. In this way, it was possible to control all the key factors of the condensate dynamics looking for the worst condition and, at the same time, without loosing the coupling effects of the car assembly. However, this method is very expensive because of the high cost of facility maintenance and use; the obvious consequence is that only a low number of tests is possible. It was then necessary to find another way for testing different project solutions and prototypes, in order to deeply understand the condensate phenomena. Automotive Lighting Italy (ALIT) designed a specific condensate test room, able to reproduce and control all the main factors involved in the phenomenon under study. The condensate test room allows for: Product Validation in house HL performances evaluation allows the adoption of corrective actions (if needed) before the test is performed in the presence of the customer; Prototype Evaluation several in house tests are possible in order to test different and/or innovative solutions for new projects; Benchmark in house tests are possible in order to evaluate competitors solutions; Simulation full availability for all necessary tests used for software calibration. Test description Condensate tests are usually divided into three main steps. A first conditioning period is followed by a condensate formation stage; after that, the condense disposal step is performed. For this last step, a time threshold is usually fixed. In Table 1, the condensate test steps are described in detail.

16 16 - Newsletter EnginSoft Year 6 n 2 Condensate tests are considered successful if, after 60 minutes from the beginning of stage 2, condensate is not visible inside the headlamp or if the percentage of lens surface covered by condensate is lower than a prescribed value. Table 1: condensate test description ALIT Condensate Test Room ALIT Condensate Test Room is a metal room with a volume of about 30m3 (see Figure 4). Glass windows allow the technicians to follow the ongoing tests. By using a dedicated hardware, it is possible to control all the main variables related to the condensate disposal process, such as: engine box. Indeed, geometric and thermodynamic effects of the engine are still too complex to be reproduced. Nevertheless, a good approximation is obtained by using an average temperature inside the engine box mock-up. Measure devices A major problem related to the condensate issue is the difficulty of an objective condensate tracking. Indeed, large variations in condensate layer thickness as well as in water droplets diameters may occur and this has a direct influence on the perception of the human eye. The use of a standard photographic camera with flash usually highlights even the smallest traces of condensate which may not be visible for the human eye. At the same time, it is not possible to measure a continuous distribution of the dew point. Several temperature and humidity probes are present inside the ALIT condensate test room, these are located in the free-area zone and inside the engine box mock-up. Moreover, it is possible to place thermal couples and moisture meters inside the headlamp in order to get punctual data. Finally, temperature distribution on the Figure 5: thermal maps on the lens at two different times Heat Transfer Coefficient (HTC) on headlamp boundary walls; Internal and external air relative humidity (RH); Internal and external air temperature; Pressure and air flow fields in the proximity of ventilation pipettes; Mission profile reproduction accounting for engine induced temperature and wind speed; Interaction between headlamp-engine assembly. ALIT condensate test room is projected to control all the main factors involved in the HTC distribution. It is possible to control external air RH and temperature. Moreover, an air speed of up to 80Km/h can be produced along the longitudinal car axe. Inside the room, an engine box mock-up reproduces the effects of the average temperature produced by the engine. Since HTC is influenced by aerodynamic effects too, the engine box mock-up reproduces the car shape (see Figure 4). At present, the effects not reproducible are represented by pressure and air flow fields inside the lens is tracked by means of an infrared camera. By combining these data together with photos and videos of condensate distribution it becomes possible to track the dew point line. Currently, it is not feasible to measure condensate thickness. Test Results The outputs of the condensate test are: thermal maps and videos shot using an infrared camera (Figure 5); condensate images and videos shot using photographic camera with flash (Figure 6); temperature and relative humidity graphs measured by the thermal couples and moisture meters placed inside the headlamp, inside the engine box mock-up and in the external environment (Figure 7). From Figure 6 it can be noticed that condensate tends to accumulate on the outer side of the headlamp (left side of the figure) which is the coldest part of the lens, as showed in Figure 5.

17 Newsletter EnginSoft Year 6 n 2-17 Figure 7: temperature and relative humidity graphs in ALIT Condensate Test Room Figure 6: condensate images at different times NUMERICAL SIMULATIONS The Numerical Method When a switched-on lamp is to be modelled, a radiation model has to be used in order to compute the source term for the energy equation and the radiative heat flux at walls. In the present work, the Discrete Transfer model is used for the directional approximation and the Grey model is used for the spectral approximation. The Gray model assumes that all radiation quantities are nearly uniform throughout the spectrum, consequently the radiation intensity is the same for all frequencies. The Discrete Transfer model assumes that the scattering is isotropic. The switched-on lamps are modelled by imposing the superficial temperature of the lamp bulb; surface temperature data come from experimental measurements. In the considered evaporation/condensation model, the liquid phase is not directly modelled. Instead, the evaporation/condensation processes occurring on the lens are modelled by means of suitable mass and heat sources for the continuity and thermal equations. The mass source term applied to the conservation law for water vapour mass in the gas is: Here is the water mass per unit area transferred between liquid and gas, A is the area of the element face where evaporation and condensation processes occur, A l is the total area of the surface where evaporation and condensation processes occur, L is the typical length scale of the process, is the diffusivity of water vapour in the air, considered equal to the air dynamic diffusivity, e is the water mass fraction at equilibrium, m f is the water mass fraction and Sh is the Sherwood number. The air volume fraction is the complement to unity of the computed vapour volume fraction. The energy source due to phase change applied to the conservation law for internal energy is: where C p is the water latent heat for vaporization/condensation. Mass and energy sources are applied only at surfaces where evaporation/condensation processes occur. In the framework of this evaporation/condensation model, it is possible to define the water mass per unit area laying on the lens as: Here the space and time dependency of the water mass per unit area is explicit. This variable allows for a precise tracking of the condensate amount laying on the lens.

18 18 - Newsletter EnginSoft Year 6 n 2 minutes rain stops and wind at 30 km/h starts blowing until the end of the simulation at 60 s. These conditions are simulated by varying external temperature and relative humidity together with HTC on the lens. The initial and boundary conditions used in the simulation are summarized in Table 2. Table 2: initial and boundary conditions Figure 8: velocity vectors on a vertical plane passing through the lamps (note that vectors are coloured with temperature distribution) Moreover, in the case of evaporation, the local mass source has to be null where local water mass per unit area is null; this is achieved by a local control of the mass source term. Results The simulation was run on 32 parallel CPUs with OS Linux CENTOS. The computational time was roughly 12 days. In Figure 8, velocity vectors on a vertical plane passing through the lamps are shown; note that vectors are Mass and energy sources are implemented in ANSYS CFX by means of properly defined functions and variables using the CEL language. The analyses were run using an upwind advection scheme and a backward Euler transient scheme was ordered first. Moreover, the time step and the convergence criteria were chosen in order to minimize the computational time without compromising result quality and method robustness. The Computational Mesh Solid and fluid domains were discretized using a tetra-prism mesh. In particular, prism layers were used inside each solid domain and outside the rear body, the lens and the lamps. A total of about elements were used to discretize the entire headlamp. Initial and Boundary Conditions At the initial time, the lamps are switched off, the temperature is 6 C and the relative humidity 95%. At the beginning of the simulation, lamps are switched on. After 20 minutes rain starts. After 40 Figure 9: time evolution of condensate mass per unit area

19 Newsletter EnginSoft Year 6 n 2-19 Figure 10: qualitative comparison between numerical and experimental results colored with temperature distribution. In Figure 9, the time evolution of condensate per unit area on the lens is presented. The strong buoyancy effect caused by the switched-on lamps can be appreciated in Figure 8. Furthermore, from the same figure, the complexity of the geometry of the inner part of an automotive headlamp may be appreciated: this is made up by a number of parts that strongly affect the inner velocity field. Moreover, from Figure 9, it can be noticed that condensate tends to accumulate on the outer side of the headlamp (left side of the figure), where heating from the lamp is limited as well as natural convection. CONCLUSIONS Because of the difficulties in measuring condensate mass on the lens, at present, only a qualitative comparison can be made; in Figure 10 such a comparison is presented. It can be noticed that the two results are in good agreement highlighting a region of condensate accumulation in the outer side of the headlamp. It has to be emphasized that some sensitivity analyses showed a strong dependency on initial and boundary conditions demonstrating the complexity of the phenomenon under study and the need of strongly controlled experimental conditions. Due to the complexity of the problem, numerical simulations are to be performed for a long period and on large meshes, so that a high computational power is needed. Nevertheless, numerical simulations are capable to give detailed information on the thermo-fluid-dynamics of the headlamp taking into account the condensation/evaporation phenomena that may occur on the lens. In particular, numerical simulations clearly highlight the critical areas of a headlamp design with respect to condensate formation and disposal. These information can be made available before any real headlamp is produced thus reducing the number of prototypes. Moreover, by superimposing numerical results and condensate images taken from the experimental tests, it is possible to correlate results and to get important information about the condensate issue in terms of distribution and thickness of the water layer. The combined use of numerical and experimental studies is a powerful tool for optimizing headlamp design and obtaining high performance headlamps. REFERENCES ANSYS CFX-Solver Modeling Guide. ANSYS CFX-Solver Theory Guide. Perry, R.H. and Green, D.W. (Editors) (1997). Perry's Chemical Engineers' Handbook, 7th Edition, McGrawhill. Kreith, F. and Bohn, M.S. (2001). Principles of Heat Transfer, Thomson Learning. Chenavier, C. (2001) Thermal Simulation in Lighting Systems - 5 Days / 5 Degrees. PAL Symposium Darmstadt, Preihs, E. (2006). Analytic Solution and Measurements of Condensation inside a Headlamp, COMSOL Conference Nolte, S. and Maschkio, T. (2007). Development of a Software Tool for the Simulation of Formation and Clearance of Condensation in Vehicle Headlamps, L- LAB. Schmidt, T. (2008). Nanotechnologies surface modifications for anti-fog applications in automotive lighting and sensor serial production, SAE 2008 Alberto Deponti, Fabio Damiani, Luca Brugali, Lorenzo Bucchieri EnginSoft S.p.A. Sergio Zattoni, Jacopo Alaimo Automotive Lighting Italia S.p.A.

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